The present invention relates to a method for the production of a molded part, especially a shell part for shaping a motor vehicle or aircraft passenger seat, using plastic material and a mold having a receiving part which can be acted upon with a working pressure sufficient for a molding process. An adhesive closing part or adhering strip or part to be molded onto the contour of the molded part is embedded in the mold with adhering elements on a support.
Conventional methods forming a molded part with an adhering strip, similar for example to EP 0 612 485 A1, lead to certain presumable results when the relevant molding process can be executed using low working pressures. This is the situation when, for example in the case of molded parts, foam material parts are involved, possibly upholstery foam material parts for seats. The molding process is carried out by feeding a soft foam into a foam mold, which can occur with comparatively low injection pressures. The adhesive closing part or adhering strip being formed by being shaped with and on the molded part during the molding process remains under the effect of only moderate working pressure.
If, on the other hand, molding processes are to be carried out which necessitate higher working pressures, such as is the case for example with the production of hard seat shells or shell parts which are produced of hard foam materials, working pressures on the order of approximately 5 to 10 bar pressure are required. Such pressure involves hard pressing, even crushing, of the adhering part found in the receiving part, leading to defective foam formation, for example, leading to the foam not conforming to the contour of the adhering part on the surface of the molded part, or leading to pervasive crushing of the adhering elements. These problems arise progressively more often the higher the working pressures, as is for example the case during molding processes by injection molding or with the processing of so-called prepregs or pre-impregnated parts. At those pressures, the molding process is carried out by pressing a respective resin mat suitable for the purpose into a hot molding arrangement, with pressures of between 30 and 150 bar. Because of the stresses arising from this process, for a long time it has no longer been possible during the molding process to laminate adhering parts onto the relevant molded part.
Objects of the present invention are to provide a method allowing shaping and molding of adhering parts onto a molded part, even when very high working pressures are required during the molding process.
The foregoing objects are provided according to the present invention with a method in which adhering part is supported against the effect of the working pressure during the molding process by a barbed hook surface arranged in the receiving part for the adhering part. The surface is formed by a plurality of projecting barbed hooks engaged in the intermediate spaces between the adhering elements of the adhering part in such a manner that its support member is placed against the points of the barbed hooks.
The barbed hooks engage between the adhering elements and together form a contact surface. The local surface pressure, as compared with the support of the adhering part, remains comparatively low because of the great plurality of points involved, even with application of greater pressure because of high working pressures. The support effect is then approximately comparable with the distribution of support in the case of a so-called bed of nails on account of the great number of points. A heavy body can be borne securely by the extensive surface contact. Since the points engage in the intermediate spaces between the adhering elements, the support occurs without danger of deformation of the adhering elements.
The barbed hook surface can be formed by a sort of scratching strip embedded in the receiving part of the relevant mold. Such scratching strip is made of a flat textile material having a plurality of U-shaped metal wires anchored therein. The wires are of high-grade steel. The open ends of the U-shaped wires in turn form the barbed hooks. The closed ends of the U-shaped wires form the anchoring parts within the flat textile material. The flat textile material can also involve a similar material, such as disclosed in DE 296 11 207 U1. In other words, it may be a material compound of multiple layers of cotton and heat-resistant polyamide, commercially available under the name xe2x80x9cNOMEX.xe2x80x9d
The supporting of the adhering part in the receiving part of the mold as provided in the present invention facilitates problem-free production of seat shells, shell parts or any other type of articles of hard foam having adhering parts or strips embedded in foam on the surface of the relevant fixture. Since the method according to the present invention can involve high working pressures, practically all available foamable materials can be processed. Additive materials can also be included, possibly barium sulfate (pearl white foam or artificial barium sulfate). Foaming processes can also be carried out with fiber reinforcements embedded in the respective foam mold.
One particular advantage of the present invention resides in that injection molded parts can also be produced with the adhering part spray-molded on the surface. Also, molded parts can be in the form of laminates. The method according to the present invention can be carried out, for example, with use of polyurethane-prepregs. A hot mold tool is used as a mold, having receiving part incorporating the barbed hook surface and embedding the adhering part. The respective resin mat is pressed into the mold tool serving as a mold at 130 to 150xc2x0 C., with working pressures of between 30 and 150 bar.
With performing the method using flowable plastic materials, the adhering part is preferably provided with a covering during the molding process to prevent the admission of plastic material into the adhesive elements. When the processing involves foamable plastic materials, it is preferably carried out in such a manner that a covering, which prevents the formation of foam, is arranged on the opposite side from the adhering elements. A predeterminable edge width of the covering projects out over the surface area of the adhering elements. The covering is connected with the support of the adhering part by adhesive and as a holding device for detachably contacting at least the parts of the foam mold surrounding the receiving part. When the covering is provided with ferromagnetic components, and magnetic field-producing devices, for example in the form of permanent magnet strips, are mounted on corresponding surface areas of the foam mold, the edges of the covering, which prevent the formation of foam projecting over the surface area of the adhering elements, in turn establish a part of a magnetic holding device for the tight and secure fitting of the adhering part to the foam mold.
As a covering which prevents the formation of foam, a fleece material with uncrosslinked polyurethane and with addition of ferromagnetic particles can be adhered with the side of the support turned away from the adhering elements. During the foaming process the plastic material, in the form of hard or soft foam, penetrates and comes into the structure of the fleece, so that it becomes an integral part of the fleece.
When a heat-reacting adhesive is used to fasten the fleece covering to the support of the adhering part, it is advantageous to process it in such a manner that the adhering part first is arranged without any covering which prevents the formation of foam on the barbed hook surface in the receiving part of the foam mold. Then, when reactant adhesive is found on the support of the adhering part or on the inner surface of the fleece covering, the fleece covering is laid out on the support of the adhering part in such a manner that the projecting edges of the fleece covering adhere magnetically to the foam mold. The foaming process is then carried out and the adhesive thereby is activated simultaneously by the heat being generated during the foaming process. Following termination of the foaming process and release of the adhering part from the mold, the adhering part becomes securely adhered with the fleece covering which has been foamed up in the mold part.
Objects of the present invention also include providing a molded part produced according to the method of the present invention, especially in the form of a hard shell part for a vehicle or aircraft passenger seat, with an adhering part, of which the adhesive elements are exposed in a surface of the molded part.